Thin film transistors (TFTs) are conventionally made on large glass substrates or plates for use in monitors, flat panel displays, solar cells, personal digital assistants (PDAs), cell phones and the like. TFTs are made in a cluster tool by sequential deposition of various films including amorphous silicon, doped and undoped silicon oxides, silicon nitride and the like in a plurality of vacuum process chambers typically arranged around a central transfer chamber. The cluster tool is typically coupled to a factory interface that includes a plurality of substrate storage cassette that holds substrates before and after processing. A load lock chamber is generally disposed between the factory interface and cluster tool to facilitate substrate transfer between a vacuum environment of the cluster tool and an atmospheric environment of a factory interface.
The positioning of glass substrates used for displays in a load lock chamber is difficult as compared to smaller, 200 mm and even 300 mm circular substrates. For example, as glass substrates often have dimensions exceeding 550 mm by 650 mm, with trends towards 1.2 square meters and larger, small deviations in position may result in significant substrate misalignment. A misaligned substrate has high probability of damage, resulting in a costly loss of the substrate. Moreover, a misaligned substrate must be manually removed from the load lock chamber, thereby requiring costly loss of production time and diminished substrate throughput.
Typically, the accuracy of substrate placement is controlled by a robot disposed in the factory interface that is utilized to move substrate's between the cassettes and the load lock. However, many end-users of cluster tools are now providing the factory interface and robot disposed therein. Thus, if the accuracy and repeatability of substrate placement by the user supplied robot is not within the designed specifications of the load lock chamber, substrate damage is likely. It would be desirable for the load lock chamber to be more compatible with regard to substrate placement so that tool components (i.e., user provided factory interfaces) may be used in order to reduce system costs while increasing design flexibility.
Therefore, there is a need for a load lock and substrate support that corrects the orientation and position of substrates placed thereon.